Integrated circuitry is typically fabricated on and within semiconductor substrates, for example relative to bulk semiconductor substrates and in semiconductor-on-insulator substrates. One exemplary technique for isolating different areas of circuitry includes the fabrication of trench isolation within the substrate, for example a bulk monocrystalline silicon substrate. For example, trenches are etched within a bulk semiconductor substrate, and thereafter filled with an insulative silicon dioxide material.
Another technique of forming trench isolation initially fills the trenches with polycrystalline silicon. Such might be doped with one or more conductivity enhancing impurities, or might be undoped. Regardless, the deposited polysilicon is typically planarized back and then wet etched to recess it within the respective trenches. Thereafter, an insulative material such as silicon dioxide is deposited to fill the remaining volume of the trenches.
One exemplary technique for wet etching the polysilicon to recess it relative to the trenches is to use an aqueous liquid etching solution, having a pH of about 12.0 to 14.0, comprising tetramethyl ammonium hydroxide. Unfortunately, uniformity in the etch in the amount of polysilicon removed from trench to trench is less than desirable, typically being on the order of a 10% to 30% difference among the trenches, and substantially independent of the location of the trenches on the substrate. Accordingly, the recess etch back using such an etching solution is not very controllable or predictable.
The invention was directed to overcoming problems and issues as described above, although such is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or limiting reference to the specification, and in accordance with the doctrine of equivalents.